The present invention relates to a method and apparatus for induction hardening elongated objects such as cutting blades for use in the manufacture of cardboard and paper materials. The manufacture of paper and cardboard often requires predetermined lengths of such materials to be cut by automated cutting machinery. This machinery employs elongated tubular cylinders having a plurality of knives or blades fastened thereto. Each knife blade comprises an elongated rectangular steel member having a sharpened edge. It is desired to provide an edge that stays sharp for the longest amount of time possible since blade replacement or refurbishment adds to the cost of manufacturing end products.
The conventional method for providing an extended life sharp edge is to induction harden the edge of the blade. However, one must ensure a consistent hardness profile across the length of the workpiece to prevent uneven wear, which would compromise the blades cutting abilities. Conventionally, an operator must periodically remove the blade at predetermined intervals during an induction hardening procedure and manually measure the hardness value. The primary disadvantage of this method is that it takes additional time for the steps of removing and re-securing the workpiece each time a measurement is taken. These additional steps prolong the manufacturing time and add to the labor costs. Additionally, by increasing frequency of the measurements (resolution) to increase the hardness consistency over the length of the workpiece, adds even more to the costs. Therefore, there is a continuing need to reduce the time and cost required to produce a cutting blade having a hardened edge that has an approximately uniform hardness value.